For high pressure liquid chromatography apparatuses, it is necessary to use a variety of devices which have to cope with numerous constraints such as high pressure (400 to 500 bar, or even 800 bar or more), corrosion under the action of the chemicals used (for example acidic or basic eluents) and perfect leaktightness at the various seals, for example. HPLC (High Pressure Liquid Chromatography) techniques have so far been very widely applied in biological or chemical analysis, for example in the analysis of amino acids. In such cases, there is a further constraint to add to those mentioned above, namely the biocompatibility of the various elements--pistons, valves, membranes, etc.--which are in contact with substances as sensitive as amino acids.
The constituent elements of HPLC apparatuses which have to safisfy such conditions include the one-way check valves located downstream and upstream of the pump feeding the apparatus with liquid under high pressure. The devices known at the present time consist essentially of a stainless steel sleeve in with tubular elements made of polymerized organic material are inserted or even crimped, the said elements being placed end-to-end in the sleeve. These elements create a hollow chamber in which a ball of appropriate size moves, the said ball being made of ruby in the most general case. The seat for the ball consists of a sapphire ring on which the ball rests when the device is in the closed position. At the opposite end of the chamber, there is an orifice whose mean diameter is substantially reduced compared with that of the chamber, the said orifice being arranged so that a certain amount of fluid can still pass through when the ball rests against this orifice (device in the open position).
In view of the various stresses described above, the elements of the device which are in contact with the fluid undergo relatively rapid degradation, which is further increased by the corrosive nature of some of the reagents used. Independently of the precautions taken, experience shows that it is not possible totally to avoid contact between reactive liquids and the inner face of the steel sleeve, in particular at the interface of the tubular elements placed end-to-end. For biolchemical analyses, traces of metals are therefore sufficient to interfere substantially with the result. Furthermore, in the devices which are being built at the present time, the use of polymeric organic material does not make it possible to obtain a geometry which favors the fluid flow, so these devices do not avoid the surges and turbulence which detract from the reliability of the system, in particular when HPLC techniques are used for analytical purposes.